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The Mineral sylvanite

Sylvanite Coating on Quartz

Sylvanite is a unique mineral that forms with both gold and silver in its structure. Sylvanite is structurally similar to Calaverite, but it contains silver in its structure in addition to gold. If less than 13.4% of silver is replaced by gold, it is no longer classified as Sylvanite, but rather Calaverite.

The name Sylvanite is derived from sylvanium, which was an original name proposed for the element tellurium. Tellurium is present within Sylvanite, and its first documented occurrence was in the Transylvania region of Romania - hence the name sylvanium.

Chemical Formula

(Au,Ag)Te₄

Color

Silver-white, whitish-yellow, gray

Crystal System

Monoclinic

Properties

Streak
Dark gray to black

Hardness
1.5 - 2

Transparency
Opaque

Specific Gravity
7.9 - 8.3

Luster
Metallic

Cleavage
1,1

Fracture
Uneven

Tenacity
Brittle

Crystal Habits

In prismatic, bladed, and columnar crystals. Also grainy, massive, encrusting, in veins, and in dendritic formations. Crystals may be deeply striated or have hopper and skeletal growths.

3D Crystal Atlas

Additional Information

Composition
Telluride of gold and silver

In Group
Sulfides; Tellurides

Striking Features
Color, crystal habits, and mode of occurrence

Environment
Low temperature hydrothermal replacement deposits.

Rock Type
Sedimentary

Uses

Sylvanite is an ore of gold and silver. It is also rare collector's mineral, with special value due to its gold content.

Noteworthy Localities

Veins and dendritic growths of Sylvanite , some with patterns, come from the Transylvania in Romania at Baia de Arieş (Offenbánya), Alba Co.; and Sacarîmb (Nagyág), Hunedoara Co. Elongated crystals often with deep striations or skeletal/hoppered growths are highly regarded from the Emperor Mine, Vatukoula, Viti Levu, Fiji.

There are several important Colorado localities of Sylvanite; most notable is the Cripple Creek District, Teller Co., Colorado. Other Colorado localities include the Keystone Mine, Magnolia District, Boulder Co.; the Jamestown District, Boulder Co., and the Bessie G Mine, La Plata Co., Colorado.